The present embodiments relate to time-of-flight (TOF) positron emission tomography (PET).
Nuclear medicine uses radiation emission to acquire images that show the function and physiology of organs, bones or tissues of the body. Radiopharmaceuticals are introduced into the body by injection or ingestion. These radiopharmaceuticals are attracted to specific organs, bones, or tissues of interest. The radiopharmaceuticals cause gamma photons to emanate from the body, which are then captured by a detector. The interaction of the gamma photons with a scintillation crystal of the detector produces a flash of light. The light is detected by an array of optical sensors of the detector.
Positron emission tomography (PET) is a nuclear medicine imaging technique that uses a positron emitting radionuclide. PET is based on coincidence detection of two gamma photons produced from positron-electron annihilation. The two gamma photons travel in opposite directions from the annihilation site, and can be detected by two opposing detectors of a ring of detectors. Annihilation events are typically identified by a time coincidence in the detection of the two gamma photons. The opposing detectors identify a line-of-response (LOR) along which the annihilation event occurred.
The quality of PET images is improved when the timing resolution supports a comparison of the arrival times of the two gamma photons. Some PET systems use the comparison to determine the time of flight of each gamma photon from the annihilation site. So called time-of-flight PET system use the time-of-flight information to determine where along the line of response the annihilation occurred. The annihilation site is thus located more accurately, improving the PET image.